The present invention relates to a vehicle electrical system comprising a generator, a voltage regulator, one or more electrical loads, and a control device operative to suppress transients due to sudden variations in the one or more electrical loads. The generator operates to provide electrical current to the electrical loads at a regulation voltage according to the voltage regulator parameters. The voltage regulator operates to maintain the system voltage at the regulation voltage by switching on/off the generator field coil in accordance with the electrical load requirements. The field coil, as is known to artisans of ordinary skill, is coupled with a diode operative to return the field current back into the field coil during the periods when the voltage regulator switches off the field coil. The field current is dissipated every time it passes through the field coil. The dissipation period is a function of the field coil parameters such as its resistance and inductance, known to skilled artisans as the RL parameter. For heavy duty generators operating at high speed and load, the dissipation period can be unacceptably long during which time the system voltage is above a threshold value. This over voltage condition may be long enough to be interpreted by the voltage regulator, equipped with an over voltage protection circuit, as a genuine over voltage condition, causing it to deactivate itself. Alternatively, the over voltage condition may be tolerated by the voltage regulator but nevertheless be long enough to the detriment of certain electrical components within the electrical system.
The control device of the present invention is coupled with an electrical energy source, such as a capacitor, and comprises a charging module which operates to maintain the voltage of the electrical energy source above the regulation voltage so as to suppress the effects of such transient conditions. In particular, the control device operates to charge, maintain, and discharge the electrical energy source, via the charging module, so that the voltage of the electrical energy source is kept at a predetermined voltage which is above the regulation voltage.
The control device is further configured to either store the electrical energy of the field coil in the electrical energy source, or provide the electrical energy in the electrical energy source to the field coil, when the output voltage of the generator differs from the regulation voltage. In particular, the control device operates to provide the electrical energy in the electrical energy source to the field coil when the output voltage of the generator is below the regulation voltage, and to store the electrical energy of the field coil in the electrical energy source when the output voltage of the generator is above the regulation voltage. Accordingly, the control device operates to suppress both under voltage and over voltage conditions which may be caused by sudden connection and disconnection of the electrical loads.
As the number of electrical components in vehicles increases, electrical power consumption increases accordingly. As a result, the vehicle electrical system must use high power generators that can produce sufficient electrical power to meet the demand. High power generators have correspondingly higher energy transients than lower power generators. Transient voltages associated with electrical load variations in such electrical systems can be detrimental to electrical components in the electrical system.
A typical vehicle electrical system includes electrical components that comprise semiconductor devices, such as power field effect transistors (FETs), smart power integrated circuits (ICs), microcontoller units (MCUs), digital signal processors (DSPs), memory, analog ICs, and numerous discrete devices. Sudden load variations in the electrical system due to sudden connection/disconnection of the electrical loads can destroy or otherwise cause malfunction in such devices. These transients are the most potentially destructive transients in the vehicle electrical system due to the combination of high voltage and high energy.
Under voltage condition occurs when one or more electrical loads are suddenly switched on and the generator is unable to produce electrical power fast enough to supply the electrical loads. Over voltage condition occurs when one or more electrical loads are suddenly disconnected and the generator is unable to dissipate the electrical energy in the generator field coil fast enough to keep the magnetic flux within an acceptable level. Although vehicle electrical systems ordinarily include one or more electrical energy sources such as batteries which, to a certain degree, improve the under voltage and over voltage conditions, extreme voltage transients still affect the power quality in such electrical systems. Furthermore, there are some applications where the vehicle electrical system does not include batteries which exacerbate the transient voltage variations due to sudden connection/disconnection of the electrical loads.
Batteries in a vehicle electrical system operate to provide electrical power to the electrical loads when the vehicle engine is turned off and/or when the vehicle engine is turned on but the generator is incapable of generating sufficient electrical power at the operating speed (RPM) to meet the demand, such as is the case when a high electrical power consuming device like an air conditioning unit is switched on. Batteries also act as reservoirs where excess electrical power can be stored, such as is the case when the air conditioning unit is suddenly switched off. Such sudden demand and supply of electrical power in the electrical system can occur even when the vehicle engine is operating at the rated RPM.
For instance, a vehicle electrical system including a generator that is rated to generate 500 Amps at 5000 RPM will, momentarily, experience a dip in the system voltage when a large electrical load is suddenly switched on due to the slow response time of the generator which may last in the order of hundreds of milliseconds. Similarly, a sudden disconnection of the electrical load at the above mentioned RPM, will give rise to a spike in the system voltage that may last for the same time period. These under voltage and over voltage conditions occur even in the presence of one or more batteries in the electrical system.
Not only are these transient conditions detrimental to the electrical components in the vehicle electrical system, repetitive battery under charge and over charge is detrimental to the batteries. Furthermore, the effects of the under voltage and over voltage conditions on the electrical components are intensified in batteryless applications. Consequently, there is a need for a control device that operates to improve the power quality of the electrical system by suppressing voltage transients due to sudden variations in the electrical loads. Although various systems have been proposed which touch upon some aspects of the above problems, they do not provide solutions to the existing limitations in providing high quality electrical power within a vehicle electrical system.
For example, in the Velhner et al. patent, U.S. Pat. No. 7,245,112, and its related patents, U.S. Pat. Nos. 7,161,330, and 7,154,249, an energy discharge apparatus is disclosed for dissipating a quantity of stored magnetic energy in a generator field coil of a brushless generator utilizing a variable impedance device. In particular, the variable impedance device is coupled in series with the generator field coil and includes one or more resistors, transistors, capacitors, and control means to vary the impedance so as to dissipate the stored magnetic energy in the generator field coil. The Velhner system operates differently from the present invention in that it utilizes a variable impedance device and means to vary the impedance to dissipate the excess magnetic energy, whereas the present invention uses an electrical energy source in which the excess electrical energy is dissipated. Furthermore, unlike the present invention, the Velhner system is too complex to operate because it requires multiple signals from multiple components, such as the generator output signal, exciter field signal, and exciter armature signal.
Isurin et al. patent, U.S. Pat. No. 7,106,030, discloses a system for controlling the excitation of a generator field coil to compensate for changes in the electrical loads. In particular the system utilizes a capacitor to store excess electrical energy from sudden disconnection of the electrical loads. However, unlike the present invention, the Isurin system does not include a charging module and thus is unable to maintain the voltage level of the capacitor at a predetermined voltage. Additionally, the Isurin system is incapable to compensate for under voltage that occurs when one or more electrical loads are suddenly switched on.
In today's modern vehicles, the vehicle electrical system comprises a large number of electrical components that consume large amounts of electrical power. Consequently, vehicle electrical systems use high power generators to meet the high electrical power requirement. Additionally, the vehicle electrical system incorporates electrical devices that are often sensitive to voltage fluctuations in the electrical system. As a result, the vehicle electrical system must provide high electrical power while minimizing the transient effects due to connection and/or disconnection of the electrical components. This requires the vehicle electrical system to be capable of rapidly suppressing any under voltage and over voltage conditions that may occur as a result of such connection/disconnection, before the electrical components malfunction or become inoperative. As a simple, yet efficient, alternative to existing technologies, the present invention offers a vehicle electrical system capable of providing high electrical power of high quality to multiple electrical components within the vehicle electrical system.